Screw compressor

ABSTRACT

A screw rotor compressor in which the high pressure ends of the rotors are provided with annular sealing edges cooperating with the high pressure end wall of the working space to provide central sealed chambers around the rotor shafts, which chambers are in communication with the low pressure side of the compressor.

United States Patent 1 1 1111 3,902,827 Schibbye 1 Sept. 2, 1975 [54] SCREW COMPRESSOR 2,705,922 4/1955 Rathman 11 418/201 3,178,104 4/1965 Williams ct al. 418/98 1 lnvemorl Benedlcms sch'bbye 3,462,072 8/1969 Schibbye 418/98 SaltSjO-Duvas Swede" 3,468,294 9/1969 Nilsson 1 1 1 418/201 [73] Assignee, Svenska Rotor Maskiner Aktiebolag, 3,491,730 1/1970 Nilsson .1 418/201 Nacka, Sweden [22] Filed: July 10, 1974 Primary Examiner-John J. Vrabiik pp NO: 487,145 Attorney, Agent, or FirmF1ynn & Frishauf [30] Foreign Application Priority Data [57] ABSTRACT July 20, 1973 United Kingdom 34620/73 A screw rotor compressor in which the high pressure [52] US. Cl. 418/79; 418/98; 418/201 ends f the rotors are provided with annular scaling [51] Folc 1/16; F01: 21/04; F04: 17/12 edges cooperating with the high pressure end wall of [58] held of Search 418/79- 97, 98, 99, 142, the working space to provide centra1 sealed chambers 418/ 20F203 around the rotor shafts, which chambers are in communication with the low pressure side of the compres- [56] References Cited son UNITED STATES PATENTS 2,531,603 11/1950 Berck 418/201 9 Claims, 2 Drawing Figures SCREW COMPRESSOR The present invention relates to a screw compressor of the type comprising two intermeshing rotors having helical lands and grooves and mounted in a casing, generally composed of'a low pressure end platemember, a barrel member and a high pressure end plate member, enclosing a'working space having low pressure and high pressure ports disposed generally diagonally thereof.

In those compressors there is a problem to avoid leakage from the working space along the rotor shafts projecting from the high pressure ends of the rotors.

Up to now this problem has been solved in the following Way. 7

In dry compressors a number of carbon rings have normally been inserted within the casing in direct contact with the rotor shafts which results in a bulky design producing a lot of friction losses.

In wet compressors, i.e. compressors with oil injection pressure oil is supplied around the rotor shafts, part of which passes to the bearings and part of which passes along the rotor shaft into the working space thus blocking any leakage of gas there along. The oil passing into the working space will, however, press strongly upon the rotor producing a considerable additional load on the thrust bearings the life of which consequently will be correspondingly reduced.

The aim of the present invention is to avoid those disadvantages of earlier types of compressors.

SUMMARY OF THE INVENTION According to the invention a sealing ring is inserted between the high pressure end plane of the rotor and the surface of the high pressure end plate member to practically or completely bridge the clearance therebetween. This sealing ring should be arranged on as large a radius as possible just to be sure that it never extends out into the area of the rotor grooves. The sealing ring might either be fixed to one of the members or carried by one of them and axially biased against the other. Preferably it is shaped as a thin annular edge projecting from the end plane of the rotor. The pressure within the volume comprised of the clearance between the rotor and the casing and radially limited by the sealing ring and the rotor shaft should further be kept as low as possible. For this reason this volume should preferably communicate with an area of the working space located within the low pressure phase of the compressor, i.e. within an area thereof where the pressure is the same as the inlet pressure or only somewhat higher which can easily be obtained as the pressure rise is rather slow during the first part of the compression. Preferably the channel is formed as a relieved portion in the surface of the high pressure end plate member. The channel can then easily be produced during the casting of the high pressure end plate member.

The invention will now be discussed more in detail and by way of example with reference to the accompanying drawings in which:

FIG. 1 is a vertical, longitudinal section through a compressor according to the invention, and

FIG. 2 is a cross-section taken along line 2 2 in FIG. 1.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENT The screw compressor shown comprises a casing 5 comprised of a low pressure end plate member 10, a barrel member 12 and high pressure end plate member 14 in which casing a working space 16 is provided substantially in the form of two intersecting cylindrical bores of the same size having parallel axes. In the low pressure end plate member and the barrel member 12 a low pressure channel 18 is provided which communicates with the working space 16 through a low pressure port 20. Furthermore a high pressure channel 22 is provided in the high pressure end plate member 14 which high pressure channel 22 communicates with the working space through a high pressure port 24.

Two intermeshing rotors, one male rotor 26 and one female rotor 28, are provided in the working space 16. The male rotor 26 is provided with four helical lands 30 which have a wrap angle of about 300. The lands have flanks the major portions of which are convex and located outside the pitch circle 32 of the rotor. The female rotor 28 is provided with six helical lands 34 which have a wrap angle of about 200. The grooves have flanks the major portions of which are concave and located inside the pitch circle 36 of the rotor.

The rotors 26, 28 are mounted in the low pressure end plate member 10 by radial bearings 38 ofthe roller bearing type and in the high pressure end plate member 14 by combined radial and thrust bearings 40 of the ball bearing type. The male rotor if further provided with a stub shaft 42 extending outside the low pressure end plate member 10 for connection to a driving motor, not shown.

The main part of the low pressure port lieson one side of the plane of the axes of the bores and the high pressure port 24 is completely located on the other side of said plane.

The barrel member 12 is provided with an pressure oil chamber 44 having a supply opening 46 for communication with a pressure oil source, not shown. This pressure oil source is normally a pump supplied with oil from an oil separator connected to the outlet channel of the compressor. From the oil chamber 44 oil is in conventional manner supplied to the working space 16 through injection nozzles 48. Oil is further delivered from the oil chamber 44 to the low pressure end radial bearings 38 through a channel 50. Oil is also delivered from the chamber 44 to the high pressure end radial and thrust bearings 40 through two channels 52.

The rotors 26, 28 are further at the high pressure ends thereof provided with annular axially projecting sealing rings 54, 56 located just inside the bottoms of the rotor grooves. The sealing rings 54, 56 are practically in contact with the facing surface of the high pressure end plate member 14. In said facing surface a relieved portion 58, 60 is cut out within an area cooperating with each rotor 26, 28. This relieved portion 58, 60 has such a radial and peripheral extent that it forms a communication between the volume enclosed inside the sealing ring 54, 56 and an area of the working space 16 located within the low pressure phase of the compressor, i.e. within an area thereof where the pressure is the same as the inlet pressure or somewhat higher as the pressure rise during the first part of the compression is practically negligible.

The special function according to the invention is that any gas leaking along the high pressure end plane of a rotor 26, 28 towards the shaft thereof is considerably reduced by the sealing ring 54, 56 and that any possibility to build up a high pressure between the rotor 26, 28 and the high pressure end plate member 14 resulting in an increased thrust force on the rotor 26, 28 is completely eliminated as the gas is immediately drained to the low pressure side through the relieved portion 58, 60.

Furthermore the lubricating oil supplied to the bearing 40 in the high pressure end plate member 14 is drained along the rotor shaft and through the relieved portion 58, 60 to the low pressure side of the compressor which simplifies the circulation of the bearing lubri' cating oil and positively eliminates the risk for the oil to produce a thrust force on the rotors 26, 28.

I claim:

1. Screw compressor, of the type comprising two intermeshing rotors having helical lands and grooves disposed within a working space having low pressure and high pressure ports disposed generally diagonally thereof and adjacent to a low pressure and a high pressure end wall of the Working space, respectively, characterized by a sealing ring surrounding the shaft of each rotor and disposed between the end plane of the rotor and the high pressure end wall of the working space, and by a drainage channel in said high pressure end wall forming a communication between the volume surrounded by said sealing ring and an area of the working space located within the low pressure phase of the compressor.

2. Screw compressor as defined in claim 1 comprising a bearing chamber along the rotor shaft housing a rotor shaft bearing and having bearing lubricating oil supplied thereto, and wherein said volume surrounded by the sealing ring communicates with said bearing chamber whereby said bearing lubricating oil is drained through said drainage channel.

3. Screw compressor as defined in claim 1, in which said drainage channel comprises a relieved portion in the surface of said high pressure end wall of the working space.

4. Screw compressor as defined in claim 1, in which said sealing ring is shaped as a thin annular edge fixed to and projecting from the end plane of the rotor.

5. Screw compressor as defined in claim 4 comprising a bearing chamber along the rotor shaft housing a rotor shaft bearing and having bearing lubricating oil supplied thereto, and wherein said volume surrounded by the sealing ring communicates with said bearing chamber whereby said bearing lubricating oil is drained through said drainage channel.

6. Screw compressor as defined in claim 4, wherein said sealing ring axially projects from the end plane of the rotor.

7. Screw compressor as defined in claim 4, wherein said thin annular projecting edge is located just inside the bottoms of the rotor grooves.

8. Screw compressor as defined in claim 4, in which said drainage channel comprises a relieved portion in the surface of said high pressure end wall of the working space.

9. Screw compressor as defined in claim 8, comprising a bearing chamber along the rotor shaft housing a rotor shaft bearing and having bearing lubricating oil supplied thereto, and wherein said volume surrounded by the sealing ring communicates with said bearing chamber whereby said bearing lubricating oil is drained through said drainage channel. 

1. Screw compressor, of the type comprising two intermeshing rotors having helical lands and grooves disposed within a working space having low pressure and high pressure ports disposed generally diagonally thereof and adjacent to a low pressure and a high pressure end wall of the working space, respectively, characterized by a sealing ring surrounding the shaft of each rotor and disposed between the end plane of the rotor and the high pressure end wall of the working space, and by a drainage channel in said high pressure end wall forming a communication between the volume surrounded by said sealing ring and an area of the working space located within the low pressure phase of the compressor.
 2. Screw compressor as defined in claim 1 comprising a bearing chamber along the rotor shaft housing a rotor shaft bearing and having bearing lubricating oil supplied thereto, and wherein said volume surrounded by the sealing ring communicates with said bearing chamber whereby said bearing lubricating oil is drained through said drainage channel.
 3. Screw compressor as defined in claim 1, in which said drainage channel comprises a relieved portion in the surface of said high pressure end wall of the working space.
 4. Screw compressor as defined in claim 1, in which said sealing ring is shaped as a thin annular edge fixed to and projecting from the end plane of the rotor.
 5. Screw compressor as defined in claim 4 comprising a bearing chamber along the rotor shaft housing a rotor shaft bearing and having bearing lubricating oil supplied thereto, and wherein said volume surrounded by the sealing ring communicates with said bearing chamber whereby said bearing lubricating oil is drained through said drainage channel.
 6. Screw compressor as defined in claim 4, wherein said sealing ring axially projects from the end plane of the rotor.
 7. Screw compressor as defined in claim 4, wherein said thin annular projecting edge is located just inside the bottoms of the rotor grooves.
 8. Screw compressor as defined in claim 4, in which said drainage channel comprises a relieved portion in the surface of said high pressure end wall of the working space.
 9. Screw compressor as defined in claim 8, comprising a bearing chamber along the rotor shaft housing a rotor shaft bearing and having bearing lubricating oil supplied thereto, and wherein said volume surrounded by the sealing ring communicates with said bearing chamber whereby said bearing lubricating oil is drained through said drainage channel. 